1. Field of the Invention
The present invention relates to an image processor having an image blurring processing function and an imaging apparatus including the same, and an image processing method.
2. Description of the Prior Art
Generally, an area of an imaging device for a so-called compact digital camera is smaller than that in a single-lens reflex digital camera, or than an exposure area of a silver-salt film in a film single-lens reflex camera. Thus, in comparison of focal lengths necessary for photographing an image at the same angle of field, the compact digital camera needs a shorter focal length than the single-lens reflex digital camera or the film single-lens reflex camera. In addition, with a constant F-number, a depth of field of a photographic optical system having a shorter focal length is deeper than that of a photographic optical system having a longer focal length.
To reduce the depth of field, the F-number has to be reduced. However, in order to reduce the F-number, a lens diameter of the photographic optical system needs to be enlarged, leading to increases in size and costs thereof which is not suitable for the compact digital camera. The compact digital camera generally has a characteristic of a deep depth of field and achieves a focus in a relatively wide range. Such a characteristic is advantageous in shooting an image at even brightness to obtain an image including a background image with a small blurring effect while it is disadvantageous, for example, in portrait shooting to obtain an image with a largely blurred background since it is very difficult to obtain such an image.
In order to deal with such a problem, for example, Japanese Patent Application Publication No. Hei 11-266388, No. 2003-37767, No. 2003-101858, and Japanese Patent No. 4136012 each discloses a digital camera which can blur a background image by image processing. The cameras disclosed in the publications change a characteristic of a filter in the image processing according to a distance between a subject and the digital camera or according to a position of a subject in an angle of field, so as to realize blurring effects with perspective.
However, in order to achieve great blurring effects only by the image processing using the filter, it is needed to perform filter processing with a large number of filters of a large filter order which needs a larger-scale processing circuit. This may cause an increase in manufacture costs and a decrease in processing speed.